In a small bowl combine yogurt, cheese and cumin; blend with fork until cheese is finely crumbled. Cover and chill at least 1 hour. Combine beef and nest 4 ingredients, mixing well. Shape into 4 patties. Cook in non stick skillet, or grill 3 inches from heat for 6-7 minutes on each side or until meat and juices are no longer pink. drain on paper towels. Place lettuce leaf, 5 slices on cucumber and beef patty on each roll half. Top with 2 tablespoons yogurt mixture and remaining half roll. Serves 4 From